Traditionally, in a compact data (information) processing device and a portable data processing device such as a slate computer, a tablet computer, and so forth, an efficiency of power use is a key technical issue. By using a memory display, e.g. an electronic paper, that consumes power only at a time of updating, as a display of such data processing device, it is possible to suppress standby power consumption such as power consumption at a time when a user browses.
As a memory equipped with such data processing device, it is possible to use a DRAM (dynamic random access memory), or the like. The DRAM has power-saving modes such as a self-refresh mode, and by using such DRAM as the memory of the data processing device, it is possible to achieve power saving by switching to such power-saving modes at a time of idling when there is no access for a certain period.
Furthermore, as a SoC (system-on-chip) for the electronic paper, i.MX50 Multimedia Applications Processor, or the like, is known.
However, in a conventional art, during an active operation, a memory display such as the electronic paper requires continuous access to a memory storing data for updating while the memory display is conducting an updating process. Therefore, it is impossible to utilize the power-saving mode of the memory and to turn off the power of the memory in such display. Especially, because a drawing time in the electronic paper is longer than that of a LCD (liquid crystal display), or the like, inability of reduction of power consumption in the memory during the drawing time heavily influences the power consumption in the whole system.